Convert to OneToOneField.

submissions/migrations/0002_auto_20150912_1657.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('submissions', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='scoresummary',
+            name='student_item',
+            field=models.OneToOneField(to='submissions.StudentItem'),
+        ),
+    ]

submissions/models.py

@@ -227,7 +227,7 @@ class Score(models.Model):
 
 class ScoreSummary(models.Model):
     """Running store of the highest and most recent Scores for a StudentItem."""
-    student_item = models.ForeignKey(StudentItem, unique=True)
+    student_item = models.OneToOneField(StudentItem)
 
     highest = models.ForeignKey(Score, related_name="+")
     latest = models.ForeignKey(Score, related_name="+")